Signature flips in time-varying $\Lambda(t)$ cosmological models with observational data

TL;DR

This paper explores signature flips in time-varying $ ext{Lambda}(t)$ cosmological models using observational data, revealing consistent accelerated expansion and analyzing different scenarios for the evolution of the universe.

Contribution

It introduces a comprehensive analysis of signature flips in $ ext{Lambda}(t)$ models with observational constraints, considering multiple scenarios for the power-law form of $ ext{Lambda}$.

Findings

Universe transitions from matter-dominated to accelerated expansion.

All models predict accelerated universe with $q_0<0$, $ ext{omega}_0<-rac{1}{3}$, $j_0>0$.

Different $ ext{Om}(z)$ diagnostics indicate quintessence or $ ext{Lambda}$CDM behavior.

Abstract

In this study, we investigate signature flips within the framework of cosmological models featuring a time-varying vacuum energy term $\Lambda(t)$. Specifically, we consider the power-law form of $\Lambda=\alpha H^n$, where $\alpha$ and $n$ are constants. To constrain the model parameters, we use the MCMC technique, allowing for effective exploration of the model's parameters. We apply this approach to analyze 31 points of observational Hubble Data (OHD), 1048 points from the Pantheon data, and additional CMB data. We consider three scenarios: when $n$ is a free parameter (Case I), when $n=0$ (Case II), and when $n=1$ (Case III). In our analysis across all three cases, we observe that our model portrays the universe's evolution from a matter-dominated decelerated epoch to an accelerated epoch, as indicated by the corresponding deceleration parameter. In addition, we investigate the physical behavior of total energy density, total EoS parameter, and jerk parameter. Our findings consistently indicate that all cosmological parameters predict an accelerated expansion phase of the universe for all three cases ($q_0<0$, $\omega_0<-\frac{1}{3}$, $j_0>0$). Furthermore, our analysis reveals that the $Om(z)$ diagnostics for Cases I and III align with the quintessence region, while Case II corresponds to the $\Lambda$CDM model.